In these years, notebook-sized personal computers having a wireless communication function or transceiver function for communications with a variety of peripheral devices have been developed. Such wireless communication function replaces cables connecting the personal computer with peripheral devices or mobile devices such as personal digital assistants (PDAs). Typically, wireless communications between a personal computer and peripheral devices, such as digital cameras, scanners and printers, are performed according to a short-distance wireless communication protocol, e.g. the Bluetooth Standard. The Bluetooth is a standard for short-distance wireless communications developed by the collaboration of Ericsson, IBM, Intel, Nokia and Toshiba. The Bluetooth uses the 2.4 GHz band (2.402 GHz–2.480 GHz) called ISM (Industrial, Scientific and Medial) band. It defines three power classes, namely, Power Class 1 of 1 mW, Power Class 2 of 2.5 mW and Power Class 3 of 100 mW. Depending on the power class employed, short and middle-distance communications over from 10 m to about 100 m can be done. The Bluetooth employs the GFSK modulation and the frequency hopping. The personal computer and the peripheral devices each have one wireless transceiver.
Some personal computers have a wireless communication ability to communicate with another personal computer or information processing device via mobile communication networks for, for example, the PDC (personal digital cellular) system, the PHS (personal handyphone system) and the CDMA system, or via various networks, e.g. a wireless LAN formed according to IEEE 802.11 in which the 2.4 GHz band (2.40–2.497 GHz) is used and the direct sequence spread spectrum system (DBPSK or DQPSK) or the frequency hopping system (GFSK) is employed. Typically, a wireless LAN is used indoors, e.g. in a building or in an office room, which is suitable for high speed data transfer, and data transfer is performed outdoors via mobile communication networks, using PDC, PHS and/or CDMA mobile units. Ordinary notebook personal computers can have a single wireless transceiver in the form of a wireless card inserted into it. Such wireless transceiver is arranged to conform with one of the above-described wireless communication systems.
Shinichi lchitsubo disclosed controlling powers for data transmission between a base station and a mobile station, in Japanese Unexamined Patent Publication No. HEI 5-75484 A laid open for public inspection on Mar. 26, 1993. According to Ichitsubo, one of the base and mobile stations detects the power level of a received RF signal from the other station. The other station sends its own transmission power level modulating it on the RF signal. The one station demodulates the transmission power level sent from the other station. Using the power level of the received RF signal and the transmission power level sent from the other station, the one station computes its own transmission power level suitable for transmission and control its transmitter according to the computed suitable transmission power. The one station also sends the transmission power level on the RF signal to the other station.
In case that the base station and the mobile station operate at different frequencies, when the mobile station stops moving at a location where propagation loss is different between transmission and reception, a feedback control is performed, in which one station sends back to the other station a value by which the transmission power level at the other station should be modified. The value sent back to the other station is dependent on the power level of the RF signal received from the one station.
This transmission power control is only applicable to a system in which the mobile station has one wireless transceiver. If one wants to use this control system for controlling communications between known wireless transceivers for known various communication conditions, it is necessary to set transmission conditions for the respective cases through extra processing. Therefore this control system cannot respond quickly to changes in communication condition.
In Japanese Unexamined Patent Publication No. HEI 7-87093 A laid open for public inspection on Mar. 31, 1995 (corresponding to U.S. Ser. No. 912,527 filed on Jul. 13, 1992), Raphael Rom disclosed a process and apparatus for implementing a protocol for controlling transmitter power in a wireless LAN. In transmitter power control disclosed in this publication, a transmitter at a first node transmits, at the beginning of the protocol, its own transmitter radiation power level in a particular field in a data packet, to a receiver at a second node. The receiver at the second node determines the quality of a received signal from the transmitter radiation power level, and computes a proposed transmitter radiation power level. The receiver, then, sends back, as a feedback signal, the computed, proposed transmitter radiation power level or a value representing the received signal quality, to the transmitter at the first node, placing the feedback signal in a particular field in a data packet. The transmitter at the first node, upon receipt of the feedback signal, adjusts its transmission radiation power level according to the proposed transmitter radiation power level or received-signal quality representative value received from the receiver at the second node.
As the system proposed by Ichitsubo, if one wants to use this control system for controlling communications between known wireless transceivers for known various communication conditions, it is necessary to set transmission conditions for the respective cases through extra processing. Therefore this control system cannot respond quickly to changes in communication condition.
The inventors of the present application expect that a plurality of different wireless transceiver modules may be built in a personal computer or inserted in the form of card into a slot formed in the body of the computer, for wireless communications with another personal computer or a plurality of peripheral devices within a building or a room or for wireless communications with a network (e.g. a mobile network access point (AP) or base station, and a wireless LAN access point). In such cases, the wireless transceivers may be disposed near to each other.
The inventors also have recognized that wireless communications between a set of a personal computer and its peripheral devices and wireless communications between another set happen to take place in the same room and at the same time.
Wireless transceiver modules like the ones described above may be provided not only in notebook personal computers, but also in desktop personal computers, handheld personal computers, personal computers of other types and other information processing devices.
A plurality of wireless transceivers built in a personal computer may be located near to each other within the computer.
Information processing devices with short-distance wireless transceivers conforming with the Bluetooth may be located at respective specific distances or locations from a master personal computer.
In particularly, when a plurality of different transceivers disposed in a small-sized information processing device such as, for example, a notebook-sized personal computer are operated to communicate with other devices simultaneously, a RF signal transmitted from at least one wireless transceiver may substantially interfere with or disturb the reception of other RF signal by other wireless transceiver. Because of small dimensions of small-sized information processing devices, such as notebook personal computers, interchannel interference may not be sufficiently reduced even if antennas for a plurality of wireless transceivers associated therewith are spaced as far as possible from each other.
Also, because various devices are disposed near to each other, a RF signal from one device may interfere with a RF signal to be received by other device.
In order to provide higher reliability for communications, the reception signal power level of each device should be as high as possible within a range predetermined for that device.
A major object of the present invention is to provide an information processing device with wireless communication ability, which can avoid or sufficiently reduce, by a simple manner, inter-channel or co-channel interference which could occur when wireless communications take place between a plurality of information processing devices with wireless communication ability.